In plasma reactors, an RF power supply provides plasma source power to the plasma chamber via an impedance matching network. The impedance of a plasma is a complex and highly variable function of many process parameters and conditions. The impedance match network maximizes power transfer from the RF source to the plasma. This is accomplished when the input impedance of the load is equal to the complex conjugate of the output impedance of the source or generator.
Accurate characterization of an impedance match network is critically important for providing a reliable, efficient, and predictable processes. Typically, characterization of an impedance match network is performed with a dummy load coupled to the output of the impedance match network in place of the plasma chamber.
Multiple frequency source power is sometimes utilized in plasma reactors. This includes multiple RF power supplies each having an associated frequency dependent matching network. The frequency dependent matching networks are connected to the plasma chamber at a common output. Band pass filters may be included between each frequency dependent matching network and the chamber to provide isolation for the different frequency power sources.
FIG. 1 shows simplified schematic of a dual frequency source power embodiment 100. A first power supply 110 is coupled to a first frequency dependent matching network 130. A second power supply 120 is coupled to a second frequency dependent matching network 140. The outputs of the frequency dependent matching networks are coupled together at a common point 150 to provide dual frequency source power across a load 160. In operation the load 160 represents the plasma chamber (not shown). FIG. 1 is illustrated with a dual frequency source 100 for simplicity. Multi-frequency source power may include two or more source power supplies and frequency dependent matching networks.
Characterization of the frequency dependent matching networks 130 and 140 is performed by inserting and removing separate dummy loads at 160, each dummy load designed to match the plasma chamber impedance at each operating frequency f1 and f2, respectively. Testing of each of the frequency dependent match networks 130 or 140 is performed separately at its associated source power frequency f1 or f2. Thus, the frequency dependent matching network 130 is characterized while operating at its associated source power supply 110 at its operating frequency f1. The frequency dependent matching network 140 is characterized while operating at its associated source power supply 120 frequency f2. Additional frequency dependent matching networks (not shown) may be similarly tested, with each frequency dependent matching network being separately tested with a separate dummy load corresponding to the particular frequency of the source power in operation for the test.